L-arginine and pycnogenal are the two active ingredients in Prelox. I've tried Prelox, and after a few weeks I notice benefits, particularly in pleasure of orgasm. (The manufacturers claim the two ingredients work synergistically.) But it tends to give me a headache, at least in combination with trazodone it does.
I've read the encouraging research of doxazosin too, and I've been on 2mg a day for some time. But I can't detect any erection-enhancing effect.
Citrulline, which I've been on for a few weeks, seems to have given me no noticeable benefits either.